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I have a VDSL telephony socket with some electronics in it. I reverse engineered the PCB, but there is one component I cannot identify at all. Look like a 0.25W TH resistor, light-blue body and a single red ring as marking. On the PCB is identified as T1 (but definitely not a transistor ;) ).

This how it looks like (the small blue guy, sry I can't zoom in more):enter image description here I also add the schematics (reverse-engineered after the PCB). The component in question is T1 (this is a simmetrical design, so no sense what is doing there): enter image description here

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  • \$\begingroup\$ Show us a picture. T never refers to a transistor (that would be Q). \$\endgroup\$
    – Hearth
    Commented Oct 3, 2023 at 13:56
  • \$\begingroup\$ Yup, done! Thank you! \$\endgroup\$ Commented Oct 3, 2023 at 14:04

2 Answers 2

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If there's a single black stripe then it's a zero-Ohm resistor (a.k.a. jumper). Remember the resistor colour stripe codes: Black is zero.

Don't ask what that jumper does there.

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  • \$\begingroup\$ Could it be taking the place of a timed fuse? \$\endgroup\$ Commented Oct 3, 2023 at 14:17
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    \$\begingroup\$ @AndrewMorton yeah, could be a replacement for a fuse or bead or something else. Maybe it's just a jumper to to run a trace over another trace (common on single-side board designs). \$\endgroup\$ Commented Oct 3, 2023 at 14:21
  • \$\begingroup\$ I updated with schematics... \$\endgroup\$ Commented Oct 3, 2023 at 14:30
  • \$\begingroup\$ The measurable resistance is 1 ohm \$\endgroup\$ Commented Oct 3, 2023 at 14:36
  • \$\begingroup\$ @ZoltánGógucz That's to be suspected from a normal DMM. The zero ohm resistor is not superconducting either, but hopefully less than 1 ohm. \$\endgroup\$
    – winny
    Commented Oct 3, 2023 at 14:56
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Mistery resolved! That component is used as a simple jumper wire because on the solder side of the PCB there is a trace crossing between the terminals. Thank you all for your contribution!

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